In this December 2011 file photo, two Kenyan army soldiers shield themselves from the downdraft of a Kenyan air force helicopter as it flies away from their base near the seaside town of Bur Garbo, Somalia. Kenya's military said Friday, Sept. 28, that its troops attacked Kismayo, the last remaining port city held by Al Qaeda-linked Al Shabab insurgents in Somalia, during an overnight attack involving a beach landing.

Nairobi, Kenya — Kenyan soldiers today launched their long-awaited offensive on the last remaining stronghold of Somalia’s Al Qaeda-allied Islamists, Al Shabab, with a pre-dawn assault that caught the enemy by surprise.

Attack boats ferried hundreds of Kenyan troops onto the beaches north of Kismayo under cover of darkness, and soldiers advanced to the city’s outskirts before Al Shabab could mount a defense.

Fierce fighting broke out, and has continued throughout the day, with Kenya’s military saying it already controls part of the city, and residents there reporting the battle has yet to enter its sandy streets.

Kismayo, with a population estimated at 200,000 people, is Al Shabab’s last major stronghold after a series of attacks by African Union (AU) peacekeepers forced them from other Somali towns over the past six months. It is widely assumed the Kenyan troops, operating under the AU mission in Somalia (AMISOM) will outgun the Islamists and that the city will fall within 48 hours.

If successful, this would mark one of the AU’s most significant military achievements and leave Al Shabab without control of any major urban center in southern Somalia. But it may result in pushing the Islamist group toward more guerrilla tactics, changing the state of play in Somalia and further punishing the population with ongoing violence.

Al Shabab is dependent on revenue from taxing imports and exports passing through the city’s port, and losing control over Kismayo could leave the Islamists bankrupt, sources say.

Some embassies in Kenya’s capital of Nairobi are already discussing the increased risk of potential Al Shabab revenge attacks after today’s operation, says one diplomatic source who asked to remain anonymous for security reasons.

'An enemy that is known'

Colonel Cyrus Oguna, spokesman for Kenya’s military described today’s assault, noting the element of surprise in their attack worked to the troops advantage. “Maritime forces from Kenya, allied with Somali national army troops, came ashore at 2 a.m. and that gave us the element of surprise that meant we saw no resistance initially,” he said.

People living in the city – 300 miles south of Mogadishu, Somalia’s capital, and 100 miles north of the border with Kenya – said Islamist defense forces did, however, fight back.

“The town is not yet captured,” says Jamac Ukun, contacted by telephone in Kismayo. Mr. Ukun says Al Shabab has deployed fighters. “I can hear the fighting, there are heavy weapons.”

Ukun notes there is no fighting in town, but “helicopters are flying over the town and they have launched several missiles on various bases. Many young men have taken their guns and are taking part in the fighting.”

Al Shabab’s radio station, Al Andalus, was back on air after about a week of silence. Many speculated the quiet meant senior commanders had already decided to leave Kismayo. Today, the station called for the city’s residents to join the fight to repel the coalition troops, Ukun says.

Hussein Hassan, a clan elder in Kismayo, said that Al Shabab was "defending the remaining part" of the city, but that the fighting sounded like it was becoming more sporadic.

An Al Shabab spokesman said that they would “defeat the invaders, God willing,” and keep control of the city.

More than 12,000 people have fled the city in the three to four weeks leading up to today’s offensive, the United Nations refugee agency, UNHCR, said.

If today’s operation is successful and Al Shabab is defeated, pushed into the countryside, the victory may be bittersweet.

“They are going to change from an enemy that is known, to one that is unknown, in terms of where they are based, how many fighters they have, and what are their tactics,” says Mr. Atta-Asamoah, from the Institute for Security Studies.